1. Field of the Invention
The invention pertains to a friction clutch, especially for motor vehicles, with a ring-shaped pressure plate which has a more-or-less radially oriented ring-shaped friction surface which can be moved axially against an opposing friction surface of a friction lining, which is carried by a support plate.
2. Description of the Related Art
When the friction linings of these types of friction clutches are new and unused, they have a much lower coefficient of friction than they do after they are worn in. As a result, it is possible for a new friction lining to slip with respect to the pressure plate after the clutch is engaged, because the force being applied by the pressure plate against the friction lining and thus also the clutch actuating force are designed for the coefficient of friction of a worn-in friction lining. To compensate for the lower coefficient of friction of the as-yet unworn friction lining, the pressing force would have to be increased, which means that the driver would be required to exert an uncomfortably large amount of force to actuate the clutch, a force which is no longer necessary after the friction lining has been worn in.
So that the friction lining can be worn in more quickly, it is known that the pressure plate can be designed with a convexly projecting friction surface. At first, a linear friction surface is formed, which leads to a very high pressure per unit area and to pronounced wear. During heavy starting accelerations, the pressure plate heats up very quickly at the friction surface, which is very narrow at first. The pressure plate can be easily deformed by this heat.